Acrylic Polymer-Based Adhesives

ABSTRACT

Acrylic polymers comprising vinyl acetate monomers, hydroxyl functional monomers and low Tg alkyl acrylate monomers are useful in adhesive compositions that find use in skin contact applications.

FIELD OF THE INVENTION

The invention relates to acrylic polymers and adhesive compositions, and end use applications thereof. In particular, adhesives which are ideally suited for skin contact applications.

BACKGROUND OF THE INVENTION

Pressure-sensitive adhesive (PSA) compositions are used for pressure-sensitive adhesive tapes, the adhesive tape comprising a backing and a PSA composition.

One field where PSA compositions find wide spread use is the medical segment, e.g., various tapes, bandages and drug delivery devices. In many such applications, such as for example skin plasters, there is direct contact between the PSA composition and the patient's skin. Adhesives for application to the skin are permanently tacky at room temperature, hold the adhered article to the skin with gentle pressure, and should be easily removed without causing pain or depositing adhesive residue.

In medical applications, the requirements imposed on the PSA composition are especially stringent, since it is necessary to avoid skin irritation and allergic reaction. Moreover, such adhesives need to adhere well to human skin during perspiration, when the weather is hot, or in an environment of draining wounds.

The continuous controlled delivery of drugs through the derma, i.e., skin, provides many advantages over other routes of administration. Transdermal drug delivery is a comfortable, convenient, and noninvasive alternative to other means of drug delivery such as by ingesting medication at fixed time intervals orally or by way of subcutaneous injection. Transdermal drug delivery systems not only allow the controlled release of a pharmaceutical product in a sustained release fashion, but reduce side effects such as gastrointestinal irritation, avoid hepatic first-pass inactivation, poor or erratic absorption from the gastrointestinal tract, and inactivation by the gastrointestinal fluids. Transdermal drug delivery also makes possible a high degree of control over blood concentrations of any particular drug. These advantages enhance patient compliance and improve the safety and efficacy of medications.

In transdermal drug delivery systems, drugs are delivered from a patch applied to the skin with a pressure sensitive adhesive. The known advantages of continuous transdermal drug delivery devices has prompted the development of transdermal drug delivery systems for the administration of a variety of drugs.

While acrylic adhesives for application to the skin are known, there is an ongoing demand and continuing need in the art for PSAs useful in medical applications. The current invention addresses this need in the art.

SUMMARY OF THE INVENTION

The invention provides polymers and adhesive compositions that can be formulated for use in medical applications, including transdermal drug delivery systems.

One aspect of the invention is directed to polymers comprising from about 30 to about 75 wt % of vinyl acetate monomers, from about 10 to about 40 wt % of hydroxyl functional monomers and from about 10 to about 70 wt % of a low Tg alkyl acrylate monomers.

Another aspect of the invention is directed to compositions comprising the polymers, including pressure sensitive adhesives for use in medical applications. The adhesive may be used in the manufacture of articles such as plasters, bandages and tapes which are adhesively adhered to the skin. The adhesive is permanently adhered to at least one substrate of the article and removable or releasably attachable to skin.

The adhesive compositions comprise acrylic polymers containing from about 30 to about 75 wt % of vinyl acetate monomer component, from about 10 to about 40 wt % of hydroxyl functional monomer component and from about 10 to about 70 wt % of a low Tg alkyl acrylate monomer component. One preferred embodiment the adhesive comprises acrylic polymers containing vinyl acetate monomers, hydroxyethyl acrylate monomers and 2-ethyl hexyl acrylate monomers. The adhesive compositions may further comprise tackifiers, plasticizers, permeation enhancers and/or therapeutic agents. The therapeutic agent, while physiologically active, may or may not be pharmaceutically active.

Yet another aspect of the invention provides articles such as plasters, bandages and tapes to be adhesively adhered to the skin. The articles comprise a backing substrate having coated to at least one surface thereof an adhesive. In one embodiment the article comprising a pressure sensitive adhesive and a therapeutic agent. In a preferred embodiment, the adhesive serves as a carrier for the physiologically active agent.

Still another aspect of the invention is directed to a method of administering a therapeutic agent to a patient comprising applying to a body surface of the patient an article comprising a backing substrate having coated to at least one surface thereof a pressure sensitive adhesive and a physiologically active agent. In one embodiment the article includes an adhesive layer into which the drug to be delivered is incorporated, a distal backing layer and a proximal release layer.

DETAILED DESCRIPTION OF THE INVENTION

Percent by weight means, unless expressly stated otherwise, percent dry weight.

The acrylic polymer of the invention comprises a vinyl acetate monomer component, a hydroxyl functional monomer component and a low Tg alkyl acrylate monomer component. It has been discovered that polymers comprising from about 30 to about 75 wt % of vinyl acetate monomer component, from about 10 to about 40 wt % of hydroxyl functional monomer component and from about 10 to about 70 wt % of a low Tg alkyl acrylate monomer component are particularly well suited for use in adhesive compositions that can be used in the production of adhesive goods such as, for example, adhesive tapes and adhesive sheets by applying an adhesive or adhesive composition to a base material such as paper, cloth or plastic film. Preferred polymers comprise vinyl acetate monomers, hydroxyethyl acrylate monomers and 2-ethyl hexyl acrylate monomers.

The acrylic polymer comprises one or more vinyl ester monomers. Preferred for use is vinyl acetate. The vinyl acetate monomers will generally be used in amount of from about 30 to about 75 weight percent, based on the total monomer weight of the acrylic polymer, preferable from about 45 to about 65 wt %.

The acrylic polymer will also comprise one or more functional monomers. Preferred are carboxy and/or hydroxy functional monomers. Primary, secondary and tertiary functional monomers are contemplated for use. Useful carboxylic acids preferably contain from about 3 to about 6 carbon atoms and include, among others, acrylic acid, methacrylic acid, itaconic acid, β-carboxyethyl acrylate, and the like. Acrylic acid, methacrylic acid and mixtures thereof are particularly preferred. Examples of hydroxy functional monomers include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate.

Hydroxy and/or carboxy functional monomers are generally used in amounts of from about 10 to about 40 weight %, based on the total monomer weight of the acrylic polymer. Preferred for use is hydroxyethyl acrylate. Particularly preferred adhesives comprise hydroxyethyl acrylate in amounts from about 15 wt % to about 25 weight %.

The acrylic polymer will also comprise at least one low glass transition temperature (Tg) alkyl acrylate monomer. Low Tg monomers are those having a homopolymer Tg of less than about 0° C. Preferred alkyl acrylates which may be used to practice the invention have up to about 18 carbon atoms in the alkyl group, preferably from about 4 to about 10 carbon atoms in the alkyl group. Alkyl acrylates for use in the invention include methyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, isooctyl acrylate, decyl acrylate, dodecyl acrylates, isomers thereof, and combinations thereof. Particularly preferred are butyl acrylate, 2-ethylhexyl acrylate and/or isooctyl acrylate, most preferably 2-ethylhexyl acrylate.

The low Tg acrylic monomers are present in amounts of from about 10 wt % to about 70 wt %, based upon the total monomer weight of the acrylic polymer.

The acrylic polymer may optionally further comprise other well known comonomers including monomers having a high glass transition temperature (i.e., a Tg greater than about 0° C.). Non-limiting examples include methyl acrylate, methyl methacrylate, ethyl acrylate and/or isobutyl methacrylate. Other comonomers can be used to modify the Tg of the acrylic polymer. Such comonomers include N-vinyl pyrrolidone, N-vinyl caprolactam, N-alkyl(meth)acrylamides such as t-octyl acrylamide, cyanoethylacrylates, diacetoneacrylamide, N-vinyl acetamide, N-vinyl formamide, glycidyl methacrylate and allyl glycidyl ether.

The adhesive compositions of the present invention optionally may include other monomers such as styrene, alkyl methacrylates such as methyl methacrylate and alkyl di(meth)acrylates.

Adhesives of the invention may also comprise blended polymers wherein the acrylic polymer is blended with and further comprises other types of polymers, including silicone polymers such as polydimethylsiloxane and polymethylphenylsiloxane and rubber polymers such as polyisobutylene and styrene-isoprene-styrene block copolymer.

In a particularly preferred embodiment, the acrylic polymer comprises vinyl acetate monomers, hydroxethyl acrylate monomer and 2-ethylhexyl acrylate. One embodiment comprises about 50 wt % vinyl acetate monomers, about 10 wt % hydroxyethyl acrylate monomers and about 40 wt % of 2-ethyl hexyl acrylate monomers. Another embodiment comprises about 60 wt % vinyl acetate monomers, about 20 wt % hydroxyethyl acrylate monomers and about 20 wt % of 2-ethyl hexyl acrylate monomers.

While a particular polymerization method is described in the examples, the polymer of the present invention may be prepared by conventional polymerization methods familiar to those of skill in the art. These methods include, without limitation solution polymerization, suspension polymerization, bulk polymerization and emulsion polymerization. In the practice of the invention, it may also be advantageous to reduce the residual monomer content, or remove or reduce solvent levels and/or other volatiles, following polymerization using methods which are known and conventional in the art. Adhesive may be applied from organic solution, aqueous dispersion, or from a melt.

As used herein, the term “pressure-sensitive adhesive” refers to a viscoelastic material which adheres instantaneously to most substrates with the application of slight pressure and remains permanently tacky. A polymer is a pressure-sensitive adhesive within the meaning of the term as used herein if it has the properties of a pressure-sensitive adhesive per se or functions as a pressure-sensitive adhesive by admixture with tackifiers, plasticizers or other additives.

Suitable tackifying agents are those known in the art including: (1) aliphatic hydrocarbons; (2) mixed aliphatic and aromatic hydrocarbons; (3) aromatic hydrocarbons; (4) substituted aromatic hydrocarbons; (5) hydrogenated esters; (6) polyterpenes; (7) mineral oils; and (8) wood resins or rosins and hydrogenated forms thereof. Levels of tackifiers is generally from about 1 wt % to about 30 wt % based on the weight of the total adhesive composition.

The compositions of the invention may include other additives known to those skilled in the art. These additives may include, but are not limited to, pigments, fillers, fluorescent additives, flow and leveling additives, wetting agents, surfactants, antifoaming agents, rheology modifiers, permeation enhancers, stabilizers, and antioxidants.

Antioxidants are typically added singly or in combination to protect the ingredients against degradation during preparation and use of the adhesive compositions and to ensure long-term thermal stability. In general up to about 1% by weight of one or more antioxidants is included in the adhesive compositions. Usually, from about 0.1% to about 0.5% by weight.

While the pressure sensitive adhesive of the invention may be used in any number of applications, e.g., labels, the adhesive is particularly well-suited for use in medical applications. The pressure sensitive adhesives find use in the manufacture of articles such as ostomy seals, adhesive tapes and bandages, wound drainage adhesive seals, wound dressings, as adherents for other products and the like that adhere to human skin and remain adherent even in a moist environment.

The adhesive of the invention is particularly well-suited for use in transdermal applications. The pressure sensitive adhesive of the invention may be incorporated into a transdermal drug delivery device designed to deliver a therapeutically effective amount of a product to the skin of a patient, e.g., to cure a skin irritation or to deliver a therapeutically effective amount of drug across the skin of a patient. The term transdermal refers to the use of the skin as a portal for the administration of drugs by topical application or for diagnostic procedures such as the monitoring of blood chemistry. The topically applied drug passes into and/or through the skin. Thus “transdermal” is used broadly to refer to the topical administration of a drug which acts locally, i.e., at the surface or within the skin, such as, for example, a blemish patch used to treat acne, and to the topical application of a drug which acts systemically by diffusing through the skin and entering the blood stream.

Transdermal drug delivery devices of the invention comprise a carrier (such as liquid, gel, or solid matrix, or a pressure sensitive adhesive) into which the drug to be delivered is incorporated, a distal backing layer and a proximal release layer. When the patient peels the release liner from the adhesive and applies the patch, the drug partitions into the stratum corneum (outer skin layer) and permeates through the epidermis and dermis.

The pressure-sensitive skin contact adhesive of the invention may be used as a carrier contact adhesive or overlay contact adhesive for transdermal patches and is non-irritating, easy to apply, and easy to remove.

The term “drug” is to be construed herein in its broadest sense to mean any agent which is intended to produce some therapeutic benefit. The agent may or may not be pharmaceutically active, but will be “bioactive” in the sense that it has an effect on the human body. The agent may be used to treat or alter a condition, which may or may not be a pathological, i.e., a disease state. “Drug”, “bioactive agent,” “preparation,” “medicament,” “therapeutic agent,” “physiological agent” and “pharmaceutical agent” are used interchangeably herein and include substances for use in the diagnosis, cure, mitigation, arrest, treatment or prevention of a condition or disease state or to affect the structure or function of the body. Skin-wellness agents that function to e.g., soften and moisturize are included in this term. The term “treatment” is used broadly to encompass prevention, alteration, cure and control of the condition.

The drug is present in a drug delivery device of the invention in a therapeutically effective amount, i.e., an amount effective to bring about a desired therapeutic result in the treatment of a condition to which the preparation of this invention is to be applied. Effective amount of a drug means a nontoxic but sufficient amount of a drug to provide the selected effect over a specific period of time. The amount that constitutes a therapeutically effective amount varies according to the particular drug incorporated in the device, the condition being treated, any drugs being co-administered with the selected drug, desired duration of treatment, the surface area of the skin over which the device is to be placed, and other components of the drug delivery device. Such an amount is readily determinable by the skilled practitioner.

The drug delivery system of the invention, in addition to the drug, may advantageously also contain an effective amount of a penetration enhancer. An effective amount of a penetration enhancer means an amount that provides a selected increase in membrane permeability, rate of administration and amount of drug.

The device of the invention is placed on the skin and allowed to remain for a time sufficient to achieve or maintain the intended therapeutic effect. The time that constitutes a sufficient time can be selected by those skilled in the art with consideration of the flux rate of the device of the invention and of the condition being treated.

The transdermal delivery devices of the invention can be made in the form of an article such as a tape, a patch, a sheet, a dressing or any other form known to those skilled in the art. The dosage system may be produced in any desirable unit form. A circular form is convenient as it contains no corners which might be easily detached from the skin. In addition to having various shapes, the dosage units produced may come in various sizes.

Depending on the design of the patch and the condition to be treated (e.g., birth control, pain management, hypertension, smoking cessation, skin condition) the patch will remain on the skin for up to an hour or more, up to about one week. In a preferred embodiment, the patch is designed to remain on the skin at the application site for about 24 hours, and to be changed daily. Preferably, the patch will be placed on the skin at a site different from the location of the previously used patches.

The term patient is used herein to include animals, both human and non-human, including companion animals such as dogs, cats and horses and livestock such as cattle and swine. Agricultural and horticultural applications are also contemplated.

Drugs that can be included in the carrier of the invention include substances capable of a local or a systemic effect when administered to the skin. Non-limiting examples include nicotine, testosterone, estradiol, salicylic acid, vitamin E, and nitroglycerin.

Veterinary drugs may also be conveniently applied using the transdermal drug delivery device of the invention, as well as agricultural and horticultural agents. It will be appreciated that transdermal drug delivery in veterinary and horticultural applications enables more exact dosing, and less waste than administration in the food/irrigation water.

A drug delivery device of the invention can be prepared by using conventional methods to apply an appropriate carrier to the backing. For example, a matrix device can be manufactured by preparing a coating formulation by mixing a solution of the adhesive in a solvent with the drug and any excipients to form a homogeneous solution or suspension; applying the formulation to a substrate (a backing or a release liner) using well known knife or bar or extrusion die coating methods; drying the coated substrate to remove the solvent; and laminating the exposed surface to a release liner or backing.

The invention will be described further in the following examples, which are included for purposes of illustration and is not intended, in any way, to be limiting of the scope of the invention.

EXAMPLES Example 1

Four samples that are representative of the invention are set forth in Table 1. Examples 2 and 3 detail how the polymers of Samples 2 and 4 were made.

TABLE 1 Monomers (wt %) Sample 1 Sample 2 Sample 3 Sample 4 Vinyl acetate 60 60 55 50 2-Hydroxyethyl 20 20 20 10 acrylate 2-Ethyl hexyl acrylate 20 40 Butyl acrylate 20 25 Tg (C.) -1 -3 -4 -20 % Solids 39.4 36.5 38.9 36.5 Viscosity (cP) 7750 11900 8850 8000 Relative viscosity 2.82 4.2 2.84 4.25

Example 2

An initial charge containing 198.0 g vinyl acetate, 20.33 g 2-hydroxyethyl acrylate, 20.43 g 2-ethylhexyl acrylate, 128.04 g ethyl acetate (solvent), and 0.23 g 2,2′-azobisisobutyronitrile (AIBN) (polymerization initiator) was prepared and charged to a 2-L 4-neck round bottom flask equipped with stainless steel stirrer, thermometer, condenser, water bath, and slow addition funnels. The initial charge was heated to reflux while stirring. At 10 minutes from the start of reflux, monomer mix containing 45.67 g 2-hydroxyethyl acrylate, 45.57 g 2-ethylhexyl acrylate, were simultaneously and uniformly added over a period of 1.5 hours. Also at 10 minutes from the start of reflux, 265.75 g ethyl acetate and 0.92 g AIBN were simultaneously and uniformly added over a period of 3 hours. At the end of the addition, the flask contents were held at reflux for 8.5 hours. At the end of the hold period, the contents were cooled to room temperature and the solution polymer discharged.

Example 3

An initial charge containing 165.0 g vinyl acetate, 10.16 g 2-hydroxyethyl acrylate, 40.85 g 2-ethylhexyl acrylate, 128.04 g ethyl acetate (solvent), and 0.23 g 2,2′-azobisisobutyronitrile (AIBN) (polymerization initiator) was prepared and charged to a 2-L 4-neck round bottom flask equipped with stainless steel stirrer, thermometer, condenser, water bath, and slow addition funnels. The initial charge was heated to reflux while stirring. At 10 minutes from the start of reflux, monomer mix containing 22.84 g 2-hydroxyethyl acrylate, 91.15 g 2-ethylhexyl acrylate, were simultaneously and uniformly added over a period of 1.5 hours. Also at 10 minutes from the start of reflux, 255.75 g ethyl acetate and 0.92 g AIBN were simultaneously and uniformly added over a period of 3 hours. At the end of the addition, the flask contents were held at reflux for 8.5 hours. At the end of the hold period, the contents were cooled to room temperature and the solution polymer discharged. 

1. An acrylic polymer comprising from about 30 to about 75 wt % of vinyl acetate monomer component, from about 10 to about 40 wt % of hydroxyl functional monomer component and from about 10 to about 70 wt % of a low Tg alkyl acrylate monomer component.
 2. The polymer of claim 1 which comprises vinyl acetate monomers, hydroxyethyl acrylate monomers and 2-ethyl hexyl acrylate monomers.
 3. The polymer of claim 2 which comprises about 50 wt % vinyl acetate monomers, about 10 wt % hydroxyethyl acrylate monomers and about 40 wt % of 2-ethyl hexyl acrylate monomers.
 4. The polymer of claim 2 which comprises about 60 wt % vinyl acetate monomers, about 20 wt % hydroxyethyl acrylate monomers and about 20 wt % of 2-ethyl hexyl acrylate monomers.
 5. A pressure sensitive adhesive composition comprising an acrylic polymer, wherein the acrylic polymer comprises from about 30 to about 75 wt % of vinyl acetate component, from about 10 to about 40 wt % of hydroxyl functional monomer component and from about 10 to about 70 wt % of a low Tg alkyl acrylate monomer component.
 6. The adhesive of claim 5 wherein the alkyl acrylate monomer component is selected from the group consisting of methyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, isooctyl acrylate, decyl acrylate, dodecyl acrylates, isomers thereof, and combinations thereof.
 7. The adhesive of claim 6 wherein the polymer comprises vinyl acetate monomers, hydroxyethyl acrylate monomers and 2-ethyl hexyl acrylate monomers.
 8. The adhesive of claim 7 wherein the polymer comprises about 50 wt % vinyl acetate monomers, about 10 wt % hydroxyethyl acrylate monomers and about 40 wt % of 2-ethyl hexyl acrylate monomers.
 9. The adhesive of claim 5 which further comprises a plasticizer, a tackifier, a permeation enhancer, a therapeutic agent, or a combination thereof.
 10. The adhesive of claim 8 which further comprises a therapeutic agent.
 11. An article of manufacture comprising the adhesive of claim
 5. 12. The article of claim 11 which is to be adhesively adhered to the skin.
 13. The article of claim 12 which is a tape, a plaster, or a bandage.
 14. The article of claim 13 wherein the adhesive comprises an acrylic polymer comprising vinyl acetate monomers, hydroxyethyl acrylate monomers and 2-ethyl hexyl acrylate monomers.
 15. The article of claim 14 wherein adhesive comprises an acrylic polymer comprising about 50 wt % vinyl acetate monomers, about 10 wt % hydroxyethyl acrylate monomers and about 40 wt % of 2-ethyl hexyl acrylate monomers. 